Afternoon Brian,
I thought of the drill and tap method also.  The flat steel I used was 1/8" (easy to cut, grind, etc.).  Just to be on the safe side, I would also place a nut to lock the threaded bolt after I screwed it in where I wanted it.  So, I would have a lock nut on each side of the threaded rod.
Guess I'm just a little overboard, but shooting the .375H&H, I was just wanting everything to stay secure with all the recoil.  This way, nothing moves.  Let me know how it turns out.
Karl